Ceramic dielectrics



Feb. 11, 1969 sHxNosU r-'uJlwARA ETAL CERAMIC DIEL'nc'rRIcs ofZ Filed June 8, 1964 FIG.

DIELECTRIC CONSTANT@ Y O/OA m S m w w M n w Mw w X n Q-VALUES FIG. 2-

Luz 03'21'505 M 4' INVENTORS BY AMM if @fpm Feb. 11, 1969 SHINQBU FUJIWARA EVAL 3,427,173

CERAMIC DIELECTRICS Filed June 8, 1964 Sheet of 2 TEMPERATURE coEr-'EICIENT SEE-Aw 0E DIELEcTRm CONSTANT United States Patent O 4 Claims ABSTRACT OF THE DISCLOSURE The present invention provides novel ceramic dielectric compositions consisting essentially of a sintered mixture of 45 to 95 molar percent barium titanate, 1 to 20 molar percent lanthanum titanium oxide La203-2'l`i02 and 1 to 54 molar percent of calcium titanate. The ceramic dielectric compositions are produced by combining barium carbonate, calcium carbonate, lanthanum oxide and titanium oxide to `form a homogeneous mixture. Such mixture is calcined in an oxidizing atmosphere at a temperature in the range of 1,l C. to 1,300 C. for about two hours. The resultant mixture is pulverized into a fine powder followed by the addition of a binder which is admixed with the powder. The mixture is formed into the desired shape and size and the resultant shape is sintered `in an oxidizing atmosphere at a temperature in the range of 1,l00 to 1,400 C. for about three hours.

This invention relates to an improvement in ceramic dielectrics.

The object of this invention is to provide ceramic dielectrics which have much greater excellence in dielectric constant and Q-value than usual ones.

The ceramic dielectrics, which have been widely used, may be classified into two types: the one mainly comprises titanium oxide and the other mainly comprises -barium titanate. Titanium oxide type dielectrics, which have been widely used as temperature compensator, have high Q-values ranging from 2000 to 3000 at high frequency, whereas their dielectric constants are small. For example, the dielectric constant of rutile ceramics which is regarded as a relatively highly practical type among the ceramics is only of the order of 114 or so.

On the other hand, barium titanate type ceramic dielectrics have large dielectric constants of more than 2000, `and low Q-value of about 150 with extremely large temperature dependence and the minimum value of temperature coeicient of dielectric constant, at the present, is approximately -6000X l0r5/ C.

The characteristic feature of the present invention is a type of ceramic dielectrics whose characteristics lie between those of the two types mentioned above. It has larger dielectric constants than those of the titanium oxide type which have small dielectric constant, and much higher Q-values than those of barium titanate type which have large dielectric constant.

That is, this invention relates to a type of ceramic dielectrics whose main components are barium titanate (BaTiOg), lanthanum titanium (IV) oxide (I a203' 2TiO2) and calcium titanate (CaTiOa), and it has dielectric constants ranging from 250 to 3000 or so, Q- values ranging from 100 to 5500 and temperature coefcients of dielectric constants ranging from -2100X 6/ C. to -9500 l0r/ C. or so.

The ceramic dielectrics in accordance with the present invention are produced by the following procedure: Stir barium carbonate (BaCOa), calcium carbonate (CaCOa), lanthanum (III) oxide (La203) and titanium (IV) oxide to be homogeneous mixture for about 20 hours, calcine the mixture in oxidizing atmosphere at the temperature 3,427,173 Patented Feb. 11, 1969 range of 1100 to 1300" C. for about 2 hours, pulverize the calcined materials into fa fine powder followed by adding a binder in solid or liquid form, in which the materials are not soluble, to bind the powder, and form the powder into disc shape in desired size with sufcient pressure for shaping, and then sinter the shaped materials in oxidizing atmosphere at the temperature range of 1100 to 1400 C. for about 3 hours.

FIGURE 1 of the accompanying drawings is a ternary diagram representing the relation between the three components of the ceramic -bodies within the present invention, that is, barium titanate (BaTiO3), lanthanum titanium oxide (La2O3-2Ti02) and calcium titanate (CaTiO3) and the dielectric constant e.

FIGURE 2 is a ternary diagram representing the relation between the three components of ceramic bodies within the present invention, that is, barium titanate (BaTiOa), lanthanum titanium oxide (La2O32TiO2) and calcium titanate and the Q-value.

FIGURE 3 is a `ternary diagram representing the relations between the three components of the ceramic bodies within the present invention, that is, barium titanate (BaTiOg), lanthanum titanium oxide (La2O3-2Ti02) and calcium titanate (CaTiO3) and temperature coelcient of the dielectric constant.

In the present invention, the range of the proportions of the three components, where the favorable properties of middle range of dielectric constant, low dielectric loss and good temperature coefficient can be obtained is limited, as can be seen in the diagrams, as follows:

(Molar percentage) Barro, 45-95 La2o3-2-rio2 1-20 Cano, 1-54 The reasons for limiting the proportions to the said values are: When the proportion of barium titanate (BaTiO3) is below 45 molar percent, dielectric constant e becomes very small, and when it exceeds molar percent, Q-value 'becomes extremely low. When the proportion of lanthanum titanium oxide (La203 '2TiO3) is below l molar percent, the eliect of addition is ineffective and when it exceeds 20 molar percent, vitrication is dil'l'lcult. When the proportion of calcium titanate (CaTiO3) is below 1 molar percent, the desired characteristics can not be obtained and when it exceeds 55 molar percent, dielectric constant e becomes small.

The following examples will give a closer insight into the present invention.

EXAMPLE II The raw materials employed are barium carbonate (BaCO3), calcium carbonate (CaCOa), lanthanum oxide (La2O3) and titanium oxide (TiOg). In the present case, barium titanate (BaTiO3) may be formed by reaction of a mixture `of barium carbonate (BaCO3) with titanium oxide (TiOa) `on tiring, calcium titanate (Ca-TiO3) may be formed by reaction of a mixture of calcium carbonate (CaCO3) with titanium oxide l(TiOZ) yon lring, and lanthanum titanium oxide (La2O3'2TiO2) may be formed from lanthanum oxide (Lagoa) and titanium oxide (TiO2) on firing.

Mix barium carbonate (BaCOB), calcium carbonate (Ca'CO3) and lanthanum `oxide (La203) with titanium oxide (TiO2) in the following proportion:

Ba-Ti03 La2O3 2TiO2 CaTiO3 :55 10: 35 (molar percentage) Stir the mixture of raw materials, to be homogeneous, for about 20 hours, then calcine the mixture in air at the temperature of 1260 C. for 2 hours. After calcination, pulverize the material so that the coarsest particles will pass a 25() mest screen and the iinest particles Will not pass 300 mesh screen, and add a small quantity of starch solution in water. Then form the powder into a disc :of desired shape of 15.`2 mm. in diameter and 0.8 mm. in thickness under a pressure of l4 Vtons per square centimeter and then sinter at the temperature of 1350 F. for 3 hours.

The characteristics of ceramic dielectric thus obtained show following values:

Dielectric constant e 366. Q-value @170. Temperature coefcient of dielectric constant -3=450 10G/ C.

EXAMPLE II The raw materials employed are barium carbonate ('BaCO3), Calcium carbonate (CaCO3), lanthanum oxide (La2O3) and titanium voxide (TiOZ). In the present case, barium titanate (BaTiO3) may be formed by reaction of a mixture of barium carbonate `(BaCO3) with titanium oxide (TiOZ) on ring, calcium titanate (SaTiO3) may be formed by reaction of a mixture of calcium carbonate ('CaCO3) lwith titanium oxide (TiO2) on iring, and lanthanum titanium oxide (LazOS-fTiOg) may be formed from lanthanum oxide (La2O3) and titanium oxide (TiO2) -on ring.

Mix barium carbonate "(BaCO3), calcium carbonate (CaCO3) `and lanthanum oxide (La2O3) with titanium oxide (TiO2) in the following proportion:

BaaTi03 I La203 =45 :10:45 (molar percentage) Stir the mixture of raw materials, to be homogeneous, for about 20 hours, then calcine the mixture in air at the temperature -of 1240 C. for `2 hours. After calcination, pulverize the material so that the coarsest particles will pass a 250 mesh screen and the finest particles will not pass 300 mesh screen, and add a small quantity of starch solution in water. Then form the powder into a disc of desired shape of 15.2 mm. in diameter and 0.8 mm. in thickness under a pressure of 4 tons per square centimeter and then sinter finally at the temperature of 1350" C. lfor 3 hours.

The characteristics of ceramic dielectric thus obtained show following values:

Dielectric constant e 250. Q-value 3991.

Temperature coeiicient of dielectric constant 2175 106/ C.

What is claimed is:

1. 'A ceramic dielectric consisting essentially of a sintered mixture `of to 95 molar percent of barium titanate (BaTiOa), 1 to 20 molar percent of lanthanum titanium loxide (La2O3-2TiO2) and 1 to '54 molar percent of calcium titanate (CaTiO3).

2. A ceramic dielectric according to claim v1 in which the proportion of barium titanate (BaTiO3) is from 45 to molar percent.

3. A ceramic dielectric according to claim 1 -in which the proportion of lanthanum titanium oxide is about 10 molar percent.

4. 1A ceramic dielectric according to claim 1 in which the proportion of calcium titanate (Ca'TO3) is from 35 to 45 molar percent.

References Cited UNlTED STATES PATENTS 3,292,062 12/1966 Gallagher et al. 106-39 2,420,692 5/1947E Waner 106-39 2,985,700 5/196'1 Johnston '106-39 FOREIGN PATENTS 5 74,5 77 1/1946 Great Britain.

OTHER REFERENCES HELEN M. MCCARTHY, Primary Examiner. 

